1. Field of the Invention
The invention relates to an image processing technique, and more particularly, to an image color processing technique.
2. Description of Related Art
In a variety of image devices, the quality of the chrominance signal is usually poor due to a variety of factors such as storing or transmitting, resulting in affecting the overall quality of the image. More particularly, the color quality of the edge of an object of the image may affect the clearness of the object displayed.
FIG. 1 illustrates a schematic view of a condition occurring in displaying the edge of an object according to a conventional image processing technique. Please refer to FIG. 1. To an image 100 displayed in an image display system, the displayed object image generally has an actual edge 102 of an object. In some conditions, the actual edge 102 of the object often has a displayed edge 104 with rainbows, causing the edge of the object blurred and then affecting the display quality. Here, the edge of the object, as known by the ordinary people, refers to the image content having textures in the displayed image. For example, the object to be displayed is a spherical object and the edge of the spherical object may have the circular texture formed with wildly changing in colors. The NTSC format is the most obvious of the above conditions of the poor quality of displaying edges. The data stored in the NTSC format is:N=Y+Cb cos(Ωt)+Cr sin(Ωt),
wherein Y is the luminance data, and the chrominance data (CbCr) is the color information in the YUV color space. The NTSC format is to form composite data from YCbCr. The separations of Y and CbCr are required to obtain the luminance and the chrominance of the image but result in the loss of the chrominance data.
FIG. 2 illustrates a schematic view of a conventional processing chrominance data method. Please refer to FIG. 2. The digital image 200 is the image data displaying the corresponding pixels of an image in the YUV color space with a pixel array. The adjacent pixel data of the odd image frame of the digital image 200 is stored in Y+C and Y−C alternatively. The next even image frame stores data in Y−C and Y+C alternatively. After the two adjacent images are mutually added or subtracted, the data of Y and C may be separated off. However, taking the pixel 204 of the object edge 202 as an example, the data of separated Y′ and C′ are both mixed with the data of C and Y because the object edge 202 usually has significant changes in luminance and chrominance. In other words, the separated Y′ and C′ have the errors as follows:Y′=Y+ΔC; C′=C+ΔY. Therefore, the displaying of the edge of the object results in poor quality.
Additionally, when the pixels are displayed in the RGB format, the arrangement of RGB subpixels generally adopts the most highly dense method to combine pixels. Therefore, the number of the green subpixels may be more than the number of the red subpixels and the number of the blue subpixels, and then the color of the image may be greenish. Hence, the displaying method in RGB may also result in distortion on the edge of the object.
How to improve the quality of the chrominance signal is one of the considerable factors of image processing.